Tài liệu Programming Embedded System I ppt

Seminar 1: “Hello, Embedded World” 1 Using the performance analyzer to test software delays 18 Strengths and weaknesses of software-only delays 19... Seminar 2: Basic hardware foundatio

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Programming Embedded Systems I A 10-week course, using C

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P3.0

P1.7 RST P1.6 P1.5 P1.4

P1.2 P1.3 P1.1 P1.0

VSS

XTL2 XTL1 P3.7 P3.6 P3.5

P3.3 P3.4 P3.2 P3.1

/ EA

P0.6 P0.7 P0.5 P0.4 P0.3

P0.1 P0.2 P0.0 VCC

P2.0

P2.2 P2.1 P2.3 P2.4 P2.5

P2.7 P2.6 / PSEN ALE

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This document may be freely distributed and copied, provided that copyright notice at the foot of each OHP page is clearly visible in all copies

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Seminar 1: “Hello, Embedded World” 1

Using the performance analyzer to test software delays 18

Strengths and weaknesses of software-only delays 19

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Seminar 2: Basic hardware foundations (resets, oscillators and port I/O) 21

Improving the stability of a crystal oscillator 31

Driving a low-power load without using a buffer 39

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Seminar 3: Reading Switches 45

Review: Basic techniques for reading from port pins 47

Example: Reading and writing bits (simple version) 49

Example: Reading and writing bits (generic version) 51

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Example: Re-structuring the Goat-Counting Example 104

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Seminar 6: Creating an Embedded Operating System 139

Timer-based interrupts (the core of an embedded OS) 144

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Seminar 7: Multi-State Systems and Function Sequences 177

Implementing a Multi-State (Input/Timed) system 195

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Seminar 8: Using the Serial Interface 211

Using the on-chip U(S)ART for RS-232 communications 219

RS-232 and 8051: Overall strengths and weaknesses 225

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Seminar 9: Case Study: Intruder Alarm System 241

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Seminar 10: Case Study: Controlling a Mobile Robot 263

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C OPYRIGHT © M ICHAEL J P ON T , 2001-2006 Contains material from:

Pont, M.J (2002) “Embedded C”, Addison-Wesley.

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P3.4 P3.5 P3.3 P3.2 XTL1

P3.1 XTL2 P3.0 RST

P3.7

P1.1 P1.0 P1.2 P1.3 P1.4

P1.6 P1.5 P1.7 VCC

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Overview of this seminar

This introductory seminar will:

• Provide an overview of this course

• Introduce the 8051 microcontroller

• Present the “Super Loop” software architecture

• Describe how to use port pins

• Consider how you can generate delays (and why you might

need to)

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Overview of this course

This course is concerned with the implementation of software (and a small amount of hardware) for embedded systems constructed using

a single microcontroller

The processors examined in detail are from the 8051 family

(including both ‘Standard’ and ‘Small’ devices)

All programming is in the ‘C’ language

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By the end of the course …

By the end of the course, you will be able to:

1 Design software for single-processor embedded applications

based on small, industry standard, microcontrollers;

2 Implement the above designs using a modern, high-level

programming language (‘C’), and

3 Begin to understand issues of reliability and safety and how

software design and programming decisions may have a

positive or negative impact in this area

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Main course textbook

Throughout this course, we will be making heavy use of this book:

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Why use C?

• It is a ‘mid-level’, with ‘high-level’ features (such as support

for functions and modules), and ‘low-level’ features (such as

good access to hardware via pointers);

• It is very efficient;

• It is popular and well understood;

• Even desktop developers who have used only Java or C++

can soon understand C syntax;

• Good, well-proven compilers are available for every

embedded processor (8-bit to 32-bit or more);

• Experienced staff are available;

• Books, training courses, code samples and WWW sites

discussing the use of the language are all widely available

Overall, C may not be an perfect language for developing embedded

systems, but it is a good choice (and is unlikely that a ‘perfect’ language will ever be created)

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Pre-requisites!

• Throughout this course, it will be assumed that you have had

previous programming experience: this might be in - for

example - Java or C++

• For most people with such a background, “getting to grips”

with C is straightforward

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Typical features of a modern 8051:

• Thirty-two input / output lines

• Internal data (RAM) memory - 256 bytes

• Up to 64 kbytes of ROM memory (usually flash)

• Three 16-bit timers / counters

• Nine interrupts (two external) with two priority levels

• Low-power Idle and Power-down modes

The different members of this family are suitable for everything from automotive and aerospace systems to TV “remotes”

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Crucially, the ‘super loop’, or ‘endless loop’, is required because we

have no operating system to return to: our application will keep looping until the system power is removed

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Strengths and weaknesseses of “super loops”

☺ The main strength of Super Loop systems is their simplicity This

makes them (comparatively) easy to build, debug, test and maintain

☺ Super Loops are highly efficient: they have minimal hardware

resource implications

☺ Super Loops are highly portable

BUT:

If your application requires accurate timing (for example, you need to

acquire data precisely every 2 ms), then this framework will not

provide the accuracy or flexibility you require

The basic Super Loop operates at ‘full power’ (normal operating mode)

at all times This may not be necessary in all applications, and can have a dramatic impact on system power consumption

[As we will see in Seminar 6, a scheduler can address these

problems.]

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Example: Central-heating controller

Central heating controller

Boiler

Temperature sensor

Temperature dial

/* Find out what temperature the user requires

(via the user interface) */

C_HEAT_Get_Required_Temperature();

/* Find out what the current room temperature is

(via temperature sensor) */

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The Standard 8051s have four 8-bit ports

All of the ports are bidirectional: that is, they may be used for both input and output

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NOTE: 0x means that the number format is HEXADECIMAL

- see Embedded C, Chapter 2

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unsigned char Port_data;

Port_data = 0x0F;

P1 = Port_data; /* Write 00001111 to Port 1 */

Similarly, we can read from (for example) Port 1 as follows:

unsigned char Port_data;

P1 = 0xFF; /* Set the port to ‘read mode’ */

Port_data = P1; /* Read from the port */

Note that, in order to read from a pin, we need to ensure that the last thing written to the pin was a ‘1’

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Creating and using sbit variables

To write to a single pin, we can make use of an sbit variable in the Keil (C51) compiler to provide a finer level of control

Here’s a clean way of doing this:

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Example: Reading and writing bytes

The input port

The output port

void main (void)

{

unsigned char Port1_value;

/* Must set up P1 for reading */

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Using the performance analyzer to test software delays

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Strengths and weaknesses of software-only delays

☺ SOFTWARE DELAY can be used to produce very short delays

☺ SOFTWARE DELAY requires no hardware timers

☺ SOFTWARE DELAY will work on any microcontroller

BUT:

It is very difficult to produce precisely timed delays

The loops must be re-tuned if you decide to use a different processor,

change the clock frequency, or even change the compiler optimisation settings

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Preparation for the next seminar

In the lab session associated with this seminar, you will use a

hardware simulator to try out the techniques discussed here This will give you a chance to focus on the software aspects of embedded systems, without dealing with hardware problems

In the next seminar, we will prepare to create your first test systems

on “real hardware”

Please read Chapters 1, 2 and 3 before the next seminar

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Seminar 2:

Basic hardware foundations (resets, oscillators and port

I/O)

Atmel89C52

XTAL 1

DS1812

12 MHz

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Typical features of a modern 8051:

• Thirty-two input / output lines

• Internal data (RAM) memory - 256 bytes

• Up to 64 kbytes of ROM memory (usually flash)

• Three 16-bit timers / counters

• Nine interrupts (two external) with two priority levels

• Low-power Idle and Power-down modes

The different members of this family are suitable for everything from automotive and aerospace systems to TV “remotes”

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Review: Central-heating controller

Central heating controller

Boiler

Temperature sensor

Temperature dial

/* Find out what temperature the user requires

(via the user interface) */

C_HEAT_Get_Required_Temperature();

/* Find out what the current room temperature is

(via temperature sensor) */

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Overview of this seminar

This seminar will:

• Consider the techniques you need to construct your first

“real” embedded system (on a breadboard)

Specifically, we’ll look at:

• Oscillator circuits

• Reset circuits

• Controlling LEDs

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• If the oscillator fails, the system will not function at all

• If the oscillator runs irregularly, any timing calculations

performed by the system will be inaccurate

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• A variant of the Pierce oscillator is common in the 8051

family To create such an oscillator, most of the components

are included on the microcontroller itself

• The user of this device must generally only supply the crystal

and two small capacitors to complete the oscillator

implementation

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XTAL

In the absence of specific information, a capacitor value of

30 pF will perform well in most circumstances

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Oscillator frequency and machine cycle period

• In the original members of the 8051 family, the machine

cycle takes twelve oscillator periods

• In later family members, such as the Infineon C515C, a

machine cycle takes six oscillator periods; in more recent

devices such as the Dallas 89C420, only one oscillator period

is required per machine cycle

• As a result, the later members of the family operating at the

same clock frequency execute instructions much more

rapidly

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Keep the clock frequency as low as possible

Many developers select an oscillator / resonator frequency that is at

or near the maximum value supported by a particular device

This can be a mistake:

• Many application do not require the levels of performance

that a modern 8051 device can provide

• The electromagnetic interference (EMI) generated by a

circuit increases with clock frequency

• In most modern (CMOS-based) 8051s, there is an almost

linear relationship between the oscillator frequency and the

power-supply current As a result, by using the lowest

frequency necessary it is possible to reduce the power

requirement: this can be useful in many applications

• When accessing low-speed peripherals (such as slow

memory, or LCD displays), programming and hardware

design can be greatly simplified - and the cost of peripheral

components, such as memory latches, can be reduced - if the

chip is operating more slowly

In general, you should operate at the lowest possible oscillator

frequency compatible with the performance needs of your application

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Stability issues

• A key factor in selecting an oscillator for your system is the

issue of oscillator stability In most cases, oscillator stability

is expressed in figures such as ‘±20 ppm’: ‘20 parts per

million’

• To see what this means in practice, consider that there are

approximately 32 million seconds in a year In every million

seconds, your crystal may gain (or lose) 20 seconds Over

the year, a clock based on a 20 ppm crystal may therefore

gain (or lose) about 32 x 20 seconds, or around 10 minutes

Standard quartz crystals are typically rated from ±10 to ±100 ppm, and

so may gain (or lose) from around 5 to 50 minutes per year

Tiêu đề	Programming Embedded System I ppt
Tác giả	Michael J. Pont
Trường học	University of Leicester
Chuyên ngành	Programming Embedded System I
Thể loại	lecture notes
Năm xuất bản	2002-2006
Thành phố	Leicester

Định dạng
Số trang	284
Dung lượng	2,48 MB